One of the first lessons you’ll ever learn when it comes to swimming is to face your fear of water.
Typically, the instructor would tell you to familiarize yourself with the water by either submerging in it or lying flat on your back in order to float.
I learned swimming on my own after battling my fear of deep water for close to 29 years. For a person who is unable to swim, asking them to lie on their back would induce a frightened state of panic.